Iran says Friday that it wants to cooperate with the West – but then it doesn't.

Some Western powers tell Iran categorically that it must accept a recently negotiated uranium-enrichment deal – but then another sounds an accommodating tone towards Tehran.

And surprise – this time it's the Europeans who are taking the tough line with Iran, while Washington signals a willingness to wait and see where negotiations might still lead.

The latest diplomatic twists and turns with Iran over its nuclear program may seem to suggest that Iran is simply employing the same stalling tactics it has used over six years of nuclear diplomacy. But what makes this time different is a serious American desire to see if the Iranian nuclear challenge can be addressed diplomatically, as well as a fractured and unstable political landscape at home that Iran's leadership must weigh in its calculations, Iran and diplomatic experts say.

"The administration is sticking by [President Obama's] game plan of letting this play out to the end of the year," says Lawrence Korb, a US foreign-policy expert at the Center for American Progress (CAP) in Washington. Administration officials are not yet convinced that negotiations can't lead to an acceptable deal with Iran to at least put off the possibility of it building a nuclear weapon, he says.

Even if talks fail, the administration sees advantages in taking the soft line for the time being, Mr. Korb adds.

"If they talked tough now, they'd have no chance of bringing the Russians and the Chinese along on new sanctions," he says. "But they're betting that by engaging Tehran now, they might be able to get more support on those sanctions later."

Questions about Iran's – and the international community's – intentions arose again Friday: Iran signaled it would accept, but then indicated it would modify, a plan tentatively agreed upon earlier this month to remove a substantial portion of Iran's low-enriched uranium stockpile to Russia and France for further enrichment. Iran appeared to balk at a plan that would remove the uranium in one large shipment before the end of the year.

Iranian President Mahmoud Ahmadinejad said Friday that Iran was ready to cooperate with the West, only to have other Iranian sources suggest later through Iranian state media that the deal would have to be changed to fly.

Iran, insisting that Western countries have not lived up to deals reached in the past, suggested that it fears the uranium would never return. So it's indicating that it may demand a step-by-step exchange – of a portion of the uranium for the return of another portion suitable for use in a Tehran research reactor.

The airing of such counterproposals suggests to some Iran experts that this is not simply Iran being Iran.

"I know people are saying, 'The Iranians like to negotiate; this is the Iranians doing what they like best' – well, maybe," says Alex Vatanka, senior Middle East analyst at IHS Jane's, the international security consulting firm. "That might be true if they didn't have the Qom revelations over their head" – referring to a secret nuclear facility revealed last month – "if they didn't have the domestic political factor and the criticisms over the postelection repression to consider, and if they didn't have Barack Obama across from them proposing serious negotiations instead of George W. Bush sounding hostile. It gives them a lot they have to consider."

That came after European Union foreign ministers took a tough line with Iran, demanding Tehran accept the enrichment deal as negotiated with the US, Russia, and France. "It's the same old tricks," Sweden's foreign minister, Carl Bildt, said following the EU meeting. "A back-and-forth for further talks."

That frustration is also evident among US lawmakers. Committees in both houses of Congress have advanced bills with broad co-sponsorship that call on Obama to get tough with Iran now by announcing new sanctions – notably targeting Iran's gasoline imports.

Congress can't force the president to adopt sanctions now, but the advancing legislation could serve the administration's purpose, say Korb of CAP. "They can say to the Iranians, 'We can only hold Congress off so long,' " he says. "It's the same with the role reversal we're seeing with the Europeans: Their getting tough can also help."

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